THIS invention relates to a process for the treatment of water streams.
Water streams, typically waste waters, and in particular acid mine drainage waters, can have pH values as low as 1.5 or 2. They also typically contain high levels of dissolved calcium, magnesium, heavy metals and sulphate. These water streams are traditionally neutralised with lime prior to discharge, and as a result they contain large quantities of calcium sulphate in solution. The discharge of these water streams into natural water courses presents a growing environmental problem.
The solubility of calcium sulphate dihydrate (gypsum) in water at 20.degree. C. is 2.35 g/l, which means that one cubic meter of water saturated with calcium sulphate would contain 0.55 kg of calcium and 1.31 kg of sulphate. In other words, a saturated acidic mine water stream flowing at 500 m.sup.3 /h, would contaminate natural water courses with 2390 t calcium and 5746 t sulphate annually.